The present invention relates generally to integrated circuits, and particularly to selecting the settings in an integrated circuit by connecting external devices, such as resistors, capacitors, and the like, to terminals of the integrated circuit.
It is common for an integrated circuit to provide a function having multiple settings that can be selected during the manufacture of a device that incorporates the integrated circuit, such as a printed circuit board. A setting is selected by applying digital inputs to terminals reserved for that purpose, for example by connecting each terminal to a high voltage, such as the power supply, or to a low voltage, such as ground. Thus for an integrated circuit using binary digital logic, a function having three possible settings requires that two terminals be dedicated to detecting the digital inputs that select one of the three settings. The number of functions and settings that an integrated circuit can provide is generally limited by the number of available terminals.
However, the terminals of an integrated circuit are a scarce resource. In relative terms, the designers of an integrated circuit are often limited less by the number of devices a package for an integrated circuit can contain than by the number of terminals the package can accommodate. For example, design and cost goals such as minimizing pin count (that is, the number of terminals of an integrated circuit) and real estate (that is, the area occupied by an integrated circuit) require that the number of terminals be minimized. Thus the number of functions and settings is often constrained by the number of available terminals.